This invention concerns a method for preparing a hydrogenation catalyst system, and a process for the hydrogenation of an olefinically unsaturated compound with hydrogen in the presence of a hydrogenation catalyst system obtained by the method of the invention.
U.S. Pat. No. 3,663,635, DE 3401983, U.S. Pat. No. 5,039,755, U.S. Pat. No. 5,132,372, EP 339986, EP 434469, EP 544304, EP 795564, EP 810231, and WO 9525130 describe catalyst systems for the hydrogenation of olefinically unsaturated compounds, and in particular for the hydrogenation of conjugated diene (co)polymers. These catalyst systems are prepared by reacting a titanocene or similar group 4 metallocene (A) (i.e., a ferrocene-like molecule based on a group 4 metal and 2 xcex75 ligands), with a metal hydride or an organometallic compound (B) and contacting (activating) the resulting catalyst mixture with hydrogen. These catalyst systems have a very high hydrogenation activity.
U.S. Pat. No. 3,663,635, for instance, describes catalyst systems for the hydrogenation of unsaturated compounds such as olefins based on titanocenes of the formula TiX2Y2 in which X represents halide, amino, hydrocarbylamino, thio, carboxylate, alkoxide or a hydrogen atom, and Y is cyclopentadienyl, indenyl, fluorenyl or allyl substituted or not, which are reacted with an aluminium hydride.
DE 3401983 describes catalyst systems for the hydrogenation of (co)polymers of conjugated dienes based on titanocenes of the formula (C5H5)2TiRRxe2x80x2 wherein R and Rxe2x80x2 may be the same or different, representing a C1-C8 alkyl or alkoxy group; C6-C8 aryl, aryloxy, aralkyl- or cycloalkyl group; a halogen atom or a carbonyl group, which are reacted with a lithium compound, i.e., a living (polybutadiene) polymer.
U.S. Pat. No. 5,039,755 describes the hydrogenation of a conjugated diene (co)polymer that is terminated with hydrogen in the presence of a titanocene to which sec-butyllithium is added.
U.S. Pat. No. 5,132,372 concerns the use of methyl benzoate as promoting agent in titanocene-based hydrogenation reactions. Further promoters are disclosed in U.S. Pat. No. 5,173,537 which describes the deactivation of lithium hydride by addition of various reagents prior to hydrogenation and titanium catalyst addition.
EP 339986 concerns hydrogenation catalyst systems consisting of at least one titanocene and a lithium compound in a molar ratio of 1/0.5 to 1/20, and optionally a reducing organometallic compound selected from the group consisting of aluminium compounds, zinc compounds and magnesium compounds.
EP 434469 describes a hydrogenation catalyst system based on at least one group 4 metallocene, at least one complex lithium, sodium or potassium compound, and optionally a polar compound or an alkali oxyhydrocarbyl compound.
EP 544304 describes a hydrogenation catalyst system based on at least one group 4 metallocene, at least one polarized compound selected from the group consisting of carbonyl group-containing compounds and epoxy group containing compounds, and an organic lithium compound.
Ligand variations have been subject of study as well. For instance, EP 795564 describes a catalyst composition based on indenyl or an indenyl-like compound as ligand, whereas EP 810231 describes catalyst systems based on heterocyclic (phosphorus containing) cyclopentadienyl-like compounds as ligand.
A zirconium-based hydrogenation catalyst system is described in WO 9525130.
Unfortunately, the activity of these catalyst systems strongly depends on a proper molar ratio of (B) over (A). It is common practice in the above documents to specify a molar ratio of (B)/(A) in the range of, e.g., 2 to 20 (e.g., DE 3401983). However, the actual operating window illustrated in the art is much narrower than this. Typically the (B)/(A) ratio at which adequate hydrogenation is achieved is in the range of 5 to 10. Apparently, at lower ratios the metallocene is insufficiently activated. At higher ratios the catalyst systems are less effective, believed to be due to increased catalyst decay. This is particularly unfortunate if the metal hydride or organometallic compound (B) is already present in high amounts in the olefinically unsaturated compounds to be hydrogenated.
It will therefore by appreciated that there is a need for an improved catalyst preparation method and an improved hydrogenation process.
From JP 8033846 a catalyst preparation method is known wherein a storage stable catalyst system is prepared by reacting the titanocene (A) with an organometallic compound (B) in the presence of a polymer containing olefinic unsaturated double bonds. The resulting catalyst mixture is in direct contact with hydrogen, and to this a polar compound is added.
The catalyst system of this Japanese patent document is produced separately from the olefinically unsaturated compound. Optimising the (B)/(A) ratio will therefore be less of a problem. Moreover, should the catalyst system should suffer from catalyst decay during hydrogenation, then additional catalyst may be withdrawn from storage and added to the hydrogenation reaction.
However, although the problem of catalyst decay would appear to be circumvented, it is not solved. Besides, if the catalyst system is to be used for the hydrogenation of a solution containing freshly prepared diene (co)polymers, than organometallic compounds still present therein need to be destroyed first to ensure the optimal (B)/(A) ratio (about 8) is maintained.
The present invention accordingly aims at providing a method for preparing a more robust catalyst system, i.e., that suffers less from catalyst decay, can be prepared in situ and at conventional but also higher (B)/(A) ratios and has increased hydrogenation activity.
Accordingly, a method is provided for preparing a hydrogenation catalyst system involving the reaction of a group 4 metallocene (A) with a metal hydride or an organometallic compound (B) at a (B)/(A) molar ratio that is larger than 10 followed by the activation of the resulting catalyst mixture with hydrogen at a hydrogen pressure p (in MPa) and at a temperature T (in xc2x0 C.), wherein a neutralising agent (C) that is capable of reacting with the compound (B) is added to the catalyst mixture
a) either prior to the activation, or
b) within t hours from the activation wherein t equals x divided by (p*T*(B)/(A)), and x=10,000.
Also, a process is provided for the hydrogenation of an olefinically unsaturated compound with hydrogen in the presence of a hydrogenation catalyst system obtained by the method described above.